1. Field of the Invention
The present invention concerns a safety feature addressing the problem of undesired full power spring expansion upon a connecting shaft failure which may occur in mid-power-spring-type brake actuators, i.e. actuators having mid-power spring brake actuation such that a service brake actuation chamber is provided between a parking or emergency brake actuator spring and a service brake apply actuator.
2. Description of Related Art
U.S. Pat. No. 3,498,174 to Schuster et al. shows a torque-limited bolt with an inner head portion which shears off at a predetermined torque.
U.S. Pat. No. 4,263,840 to Herrera concerns a safety brake mechanism including a spring brake housing with a collapsible sleeve intended to center a spring with respect to a diaphragm.
U.S. Pat. No. 5,507,093 discloses a forged steel connecting rod with a notch formed near the crankshaft bore. During a forging process, the material is forced back into the notch to form a weakened crack area so that the rod will break along the crack and form two complimentary pieces at the crankshaft bore. These pieces would not need machining and would be held together by bolts in the final assembly.
U.S. Pat. No. 5,655,431 to Pierce et al. relates to a nut and bolt assembly for a spring brake configured so that the nut will not rotate with respect to the bolt. The nut is designed so as to have a lower torque than the bolt so that excessive torque will not be passed through. A seal is also provided to prevent contamination of the spring brake assembly.
U.S. Pat. No. 5,685,200 to Baumann concerns a metal brake pressure rod connecting a plastic pedal to a brake cylinder. The brake pressure rod has a pre-designed buckling point so that failure of the rod occurs before failure of the pedal.
U.S. Pat. No. 6,217,222 to Mattson et al. shows a bearing with a notched surface formed to ease fracturing of a part into multiple pieces. The notches are shaped such that the fractures are separated into regions and provide clean surfaces after fracture.